OpenStack -- co-founded by Rackspace and NASA in 2010 -- certainly has the buzz, what with partnerships with AT&T, HP and IBM, to name a few, all of which have promised to use OpenStack as the base for their private cloud offerings.

CloudStack boasts $1 billion worth of business transactions annually running across their clouds since Citrix released the code (Citrix picked up the technology in its 2011, $200 million purchase of Cloud.com) into the Apache open source realm in April 2012.

And Eucalyptus -- the longest-standing open source project of the three -- is banking on its very tight technical ties to Amazon Web Services (AWS) to convince enterprises to go the hybrid route, running their private clouds on the Eucalyptus stack and seamlessly bursting into the Amazon public cloud when necessary.

Those are the strategic battle cries as the factions spar for positioning as the open source infrastructure as a service (IaaS) stack most tapped into for building enterprise private clouds.

According to a study on data center expansion plans by Campos Research & Analysis and paid for by data center solution provider Digital Realty Trust, three in five respondents -- 300 IT decision makers at large corporations in North America were interviewed for the study – said that building a private cloud was a primary impetus for their future data center build-out plans.

According to a new forecast report by IDC, worldwide spending on hosted private cloud (HPC) will grow to be more than $24 billion by 2016.

While most independent sources interviewed for this story contend that OpenStack is a likely front runner, they all refused to pick an ultimate winner, given that both the definition of private cloud and statistics about the rate at which enterprises are deploying and taking advantage of private clouds have been slippery little devils to pin down.

“What I can say, though, is that having three open source cloud stack options jockeying for position as the best one out there does bode well for one of them getting to widespread adoption in the enterprise in the future,” says Aneel Lakhani, research director for virtualization and cloud at Gartner.

Open source cloud platforms are attractive for the same reasons Linux took hold, low cost point of entry and the prospect of application portability.

Deep dive into the differences

There are certainly technical differences between the three open source stacks. Independent cloud application development consultant Daniel Kranowski of Business Algorithm, in a talk at the JavaOne conference in late last year, gave a thorough comparison of the stacks based on their architecture, installation, administrative capabilities, security and high availability.

Kranowski described CloudStack as having a monolithic architecture, installation processes that required a medium level of time and expertise, a strong GUI and Amazon EC2-like command line interface, offering baseline security ties and offering some load balancing capabilities.

Kranowski said that Eucalyptus’ architecture comprises five parts, similar to AWS, a medium level of install difficulty, and a limited administrative GUI that needs quite a bit of help from a command line counterpart. Also, Eucalyptus has a key management model of security in which the five architectural components need to register with each other.

He described OpenStack as having a fragmented, distributed architecture, rated it as difficult to install, and said it gets driven by multiple CLIs, has a strong, token-based security system, and uses Swift – the OpenStack massively scalable redundant storage system as the linchpin of its high availability story.

But these technical differences are not getting as much attention as the momentum markers each camp pushes to prove why it is better suited for enterprise private cloud business.

For example, the OpenStack camp boasts that at its semi-annual OpenStack Summit in mid-April, there were 3,000 conference attendees, 500 code contributors and 8,500 downloads of it most recent code release in just three weeks.

OpenStack competitors are quick to point out that of all three stacks, OpenStack is the most difficult to piece together. “OpenStack is really a technology, not a product,” says Peder Ulander, vice president of product marketing for cloud platforms at Citrix.

JC Martin is a cloud architect at eBay, which currently runs 50% of the site’s business on a private cloud. Martin explains the current OpenStack-based cloud is his company’s second generation, its first one was built on a home-grown platform. He adds that his team wanted to move to open source last year and after an extensive evaluation of the options, selected OpenStack and deployed it themselves.

“You do need a talented group of developers that have experience in day-to-day systems administration and know how to write service automation software and then write code that exposes those services to both IT staff and business end users,” Martin says.

Lauren Nelson, Forrester's private IaaS cloud lead, agrees with Ulander and contends that enterprises will most readily consume OpenStack via a provider, as opposed to downloading a distribution themselves and standing up their own private cloud internally.

“I know of very few companies that will want to pull their top development talent off a revenue-generating project to build an IaaS internally,” Nelson says.

But there are literally dozens of companies that either have built or have announced plans for OpenStack-based IaaS products, and each has to demonstrate a strategic advantage for its customers.

Portability concerns

Some analysts question whether those strategic features will over time become propriety features that would curtail the whole point of having an open source-based stack: being able to avoid vendor lock-in because writing a cloud application to an open standard is supposed to provide some portability options.

"The race is basically over unless the vendors who are building their private cloud offerings on OpenStack decide to get greedy and built proprietary features that could give them an appealing edge in that market, but could also lead to some levels of OpenStack interoperability issues down the road," Enterprise Management Associates analyst Torsten Volk says.

Gartner’s Lakhani says portability is a distant prospect for most enterprises looking to build a private cloud today. He argues it is going to be at least 12 to 18 months before private cloud users are going to really demand that they be able to run applications across OpenStack platforms.

Volk did point to the OpenStack Foundation’s efforts to ramp up platform certification efforts to help preclude any issues that might lead to users getting locked into one OpenStack platform or another due to application dependencies.

Industry watchers say Eucalyptus’s strength and its weakness are its ties to Amazon. The company – which brags of tens of thousands of downloads of its Amazon-compatible cloud software and $55.5 million in venture capital money (including $30 million picked up last year) -- says it offers API parity with 90% of the popular services offered by AWS including EC2, S3, EBS, IAM, Autoscaling ELB and CloudWatch. So an application running on a Eucalyptus private cloud using its AWS compatible services could burst out into the Amazon cloud using those same services.

“When a customer puts in one of our clouds, they become an instant member of the Amazon ecosystem,” says Eucalyptus CEO Marten Mickos.

Forrester’s Nelson lauds Eucalyptus for having a very complete technology offering that is much more readily consumable when compared to OpenStack. That does translate to a strong hybrid cloud proposition, which many enterprises are considering.

“But on the other hand you’ve got Amazon continuously downplaying the need for private cloud, so that might not bode well for Eucalyptus’ plans,” Nelson says.

The Apache CloudStack offering also has strong ties to Amazon public clouds in that it offers an API translator so that applications written for CloudStack can also run in AWS.

And Citrix’s Ulander argues that its success with larger deployments – which admittedly tend to be mostly service provider installations – “shows that our stack has gone beyond the typical greenfield and dev/test deployments and into supporting revenue-generating applications.”

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